- United States Geological Survey data shows earthquake swarms continue around the world's largest active volcano, Mauna Loa, on the Big Island of Hawaii. Such unrest could be a precursor to an eruption not seen in decades. In the 24 hours ending Tuesday, at least 50 quakes measuring 3.0 magnitude or below rattled Mauna Loa. Geologists are worried the quakes are signs magma churns underneath the volcano could spark an eruption.....Â